1. Field of the Invention
The present invention is directed generally to an exposure device for use with a copying machine or the like, and more particularly, to an exposure device with a filter for absorbing rays of heat produced by a light source.
2. Description of the Prior Art
A typical arrangement of a copying machine is that: an original is placed on an original board composed of transparent hard glass; the original undergoes an exposure via the original board by means of a light source such as a halogen tungsten lamp; and the light reflected therefrom is led again via the original board to an exposure point to expose a photosensitive material (a photosensitive/pressure-sensitive sheet, a photoconductive drum or the like), thus forming a latent image. Beams of light emitted from the light source, however, have wavelengths containing the heat rays (near infrared rays), and in some cases the original board may be heated up for a long stretch of exposure. To cope with this, preventing the heat-up of the original board hitherto involved the use of a filter, disposed in front of the light source, for absorbing or reflecting the heat rays (towards the light source).
The thus arranged exposure device, however, presents such problems that repetitions of exposing/stopping cause the filter to be heated up and cooled down repeatedly. The repetitions thereof lead to a fragility of the filter, resulting in cracks or warps thereof.
As a countermeasure against such problems, the filter is split into a plurality of blocks to lessen the distortions caused by the repetitions of heating/cooling process (the arrangement being disclosed in Japanese Patent Laid-Open No. 259635/1988).